150-BAUD PRIVATE LINE CHANNELS

Transcription

1 BELL SYSTEM Plant Series PRACTCES SECTON ssue, JUY 970 AT&TCo Standard 50-BAUD PRVATE LNE CHANNELS NTERFACE SPECFCATONS. DESCRPTON GENERAL.0 The purpose of this specification is to define the interface of the 50-Baud Private Line Channel as presented to Customer-Provided Terminals (CPT)..02 These Private Line Channels are capable of transmittingtwo state (%-mrk-space, binary ) signals at speeds up to 50 Bauds for teletypewriter, data, metering, supervisory control and miscellaneous signaling purposes. The minimum signaling element length permissible on 50-Baud Channels is 6.67 milliseconds Baud Service is different in nature than the familiar voiceband private line and DDD networks. t consists of ac or dc terminal links interconnected by networks of narrow band tandem link transmission facilities. These private line channels are half or full duplex. There will be no overall end-to-end supervision (knowledge of circuit continuity) and the interface to business machines will be Electronics ndustries Association (EA) specification RS-232B type. The send and receive data leads of this interface will be compatible with existing voiceband private line services although the supervisory leads may not function exactly the same. The meaning of this is clarified in detail in the lead-by-lead description of the interface that follows. Although the type of local loop facilities and transmission equipment arrangement provided by the Telephone Company will be subject to local conditions, the interface to the CPT will perform in essentially the same manner. PHYSCAL.o4 There are several possible transmission equipment arrangements for 50-Baud Channels..05 One basic transmissionequipment arrangement consists of the 820 D Data Auxiliary Set (DAS) for single station arrangements or an 820E DAS for multiple set arrangements. These Data Auxiliary Sets may be internally equipped with Data Sets 08- or 09-type by the Telephone Company. An 820D Data Auxiliary Set is required with each Data Set 08- or 09-type for private line service at single station installations. The 820D DAS provides the housing, power, and interface connector for the data set and performs additional operating functions as described in Paragraph Figure 4 is a photograph of this unit. For multiple set installations, the above functions are performed in an 820E DAS, illustrated in Figure 7, which may be mounted in either a relay rack or a multiple set cabinet such as those shown in Figures 8A and 8B. Two basic transmission systems are used with these first arrangements; one system uses ac transmission and the other low current dc transmission. The ac system (Data Set 08-type) will permit half-duplex (HDX) and fullduplex (FDX) operation over all loop lengths whereas the dc system (Data Set 09-type) is designed for HDX operation for those stations normally within the local exchange area of a hubbing office or for short-haul station-to-station circuits (maximum loop of 2000 ohms or.0 uf)..06 A second basic transmission equipment arrangement is interim in nature and consists of an 86-type Data Auxiliary Set plus a 30-type teletypewriter subscriber set arranged for 50-Baud Channel use. The 86 Data Auxiliary Set acts to convert the signals of the 30-type TY subscriber set to the signals specified by EA Specification RS-232B. n addition to conversion of the send and receive data signals, the 86 DAS provides the other control signals required for operation with the CPT S. The 86 DAS may be operated on a half-duplex or on a full-duplex AmericanTelephoneand Telegraph Company,970 Printed in U.S.A. Page

2 [ SECTON The 86 Data Auxiliary Set is packaged either in t an 86A single unit housing (see Figure 4) or in i an 86B multiple unit housing for up to 0 units! (See Figure 5), depending on the number of 50 Baud Channel terminations provided. The 30C! Subset is normally wall or floor mounted in its case as shown in Figure 6..o7 Where a large number of channels are to be terminated at a single location, the physical [ arrangements of the equipment arrangements may t vary due to space and maintenance considerations. [ Therefore, it is strongly recommended that these be discussed with the Telephone Company representatives well in advance of installation The general term Data Communication Equipment(DCE) will be used in this document hereafter to designate all of the complete transmission equipment arrangements provided by the Telephone Company and described in Paragraphs.04,.05 and.06. The size and weight of the arrangements are shown in Table A. POWER REQUREMENTS.o9 The customer must provide a receptacle supplying continuous 7 volt, 60 Hz ac power. The regulated power supplies provided in the DCE will work properly over a frequency deviation of Hz and a voltage range of 05 to 29 volts. The DCE is equipped with a remountable, 0-foot long gray cord equipped with a U-bladeground type plug. The power receptacle provided must accept such a plug and supply a valid ground to the ground pin. t is preferred to have this ground the same as the one used by the CPT. The power consumption per channel of the 820-type DAS equipment arrangements will be less than 5 watts. The 30-type subset plus 86 Data Auxiliary Set arrangement draws about 70 watts per channel. ENVRONMENT The DCE will operate properly over an ambient room temperature range of 4W to 2(YF and over a relative humidity range of 20 per cent to 95 per cent. Page 2 2. NTERFACE-ELECTRCAL 2.0 nterface Connector The CPT equipment should be equipped with a cable terminating in a Cinch or Cannon DB plug mounted in a Cinch DB hood assembly. Normally the cable should not exceed 50 feet in length. 2.o2 Pin Assignments in the interface connector are shown in Table B and in Figure 3. DATA COMMUNCATON EQUPMENT (DCE) EA NTERFACE 2.03 General All interface circuits between a CPT and the DCE (Figure 3) should be designed to meet the EA Standard RS-232B Functional Description A description of the required operation of the interchange leads and the signals appearing on each are as follows: Pin ) AA-Protective Ground: Electrically bonded to the machine or equipment frame and ac power service ground. Pin 2) BA Transmitted Data: The BA circuit is designed to accept serial binary data from the CPT. The DCE sends a marking signal to the line facility when the EA connector is removed or when the CPT power is OFF. Pin 3) BB Received Data: The BB circuit is designed to deliver serial binary data to the CPT. The BB circuit is held marking when received carrier or line current is not detected by the DCE. Pin 4) CA Request to Send: The CA circuit is directly connected to the Clear to Send (CB) circuit.

3 SS, SECTON 32-O-O TABLE A # OF 50 BAUD CHANNEL TERMNATON WEGHT OF DATA AUX. SET OR EMPTY CABNET DMENSONS (NCHES) WDTH DEPTH HEGHT Mounting Woil (w) Floor Tablo (T) Cabinet (C), 820-Type Data Auxiliary Sets equipped with Data Sets 08 or 09-type 820D Data Auxiliary Set -/2 # X 5-/2 X 0-/2 (T) 820E Data Auxiliary Set up to 3 e 22-/2 # 23 X 8-3/4 X 6 (c) Associated Cabinets KS 2008 List List 2 List 3 List 4 up to 3 Up to 6 up to 9 up to 2 4-/2 # 7-/2 # 23-/2 # 27-/2 # 24x2x 24x2x8 24x2x24 24x2x30 KS Up to # 34X 30-/2 X Type Auxiliary Sets 86A Data Auxiliary Set 86B Data Auxiliary Set 30C Sub Set with Cover Associated Cabinets KS 2008 List List 3 KS up to 0 up to 0 up to 20 up to This is a maximum based on space in the cabinet, this quantity should be reduced and the telephone -/2 # : 4-/2 # 23-/2 # 300 # X 5-/2 X 0-/2 2 x 9-/4 x 9 26 X 9-/2 X 6-7/8 24x2x 24x2x24 34 X 30-/2 X 72 (T,W) (c) (F,W) f room temperature exceeds 90 degrees Fahrenheit, company should be consulted, Pin 5) Pin 6) Pin 7) Pin 8) CB Clear to Send: The CB circuit is directly connected to the Request to Send (CA) circuit. CC Data Set Ready: The CC circuit presents an ON signal at all times except for the following conditions: a) When the power to the DCE is off. b) When the DCE is in either a test mode or local mode if implemented. (CC circuit held OFF) AB-Signal Ground: Establishes the common reference potential for all interchange circuits except circuit AA. CF Data Carrier Detector The CF circuit delivers an ON signal to the CPT when the DCE is receiving carrier or line current and an OFF when received carrier or line current is not detected by the DCE. Pin 2) CX Local Mode: The 820D or 820E DAS may be placed in the local mode as described below by an ON signal on the CX circuit. The local mode will not be initiated from an open circuit condition caused when the CPT power is OFF or when the EA connector is removed. DATA ~CATON EQWPMHW (~~ONAl FUNCTONS 2.05 n addition to providing the above interfaces, the DCE provides the functions described below. Page 3

4 SECTON TABLE B ALLOCATON OF PNS AT THE CUSTOMER NTERFACE PN NUMBER , 3 to 25 Note CRCUT DESCRPTON AA Protective Ground BA Transmitted Data BB Received Data CA Request to Send CB Clear to Send cc Data Set Ready AB * Signal Ground CF Data Carrier Detector (Telephone Co. use only) Data Set Test ( +P) (Telephone Co. use only) Data Set Test ( P) Cx Local Mode (Note ) Not used in this application : Available only with 820D or 820E DAS equipment arrangements. (See Paragraph 2.05) A. Local Copy (2) When used for HDX service, the DCE provides local copy on the BB circuit of data sent on the BA circuit. When receiving local copy, the DCE passes received spacing signals (breaks) over the BB circuit to the CPT. There is an installer s option on the DCE to disable local copy if it is not desired. B. Test Mode As an aid in determining whether trouble is located in the local ac terminal link including the DCE or in the CPT, a Test Mode is provided on the 86 DAS and the 820 DAS arrangements. This mode permits the telephone company to check both the send and receive transmission path from the serving test center on a loop-back basis. The test mode of the 820-type DAS is inoperable when equipped with the half-duplex dc Data Set 09. When the DCE is placed in the test mode by operation of the Test key, it acts as follows. Where differences exist between the various DCE arrangements, these are indicated. () Connects the BB circuit (Received Data) to the BA circuit (Transmitted Data) in the DCE. (3) (4) (a) the 820 DAS Arrangement Opens BA circuit on the data set from the BA circuit of CPT. (b) 86 DAS Arrangement Opens the BA circuit on the data set from the BA circuit of the CPT and, in addition, terminates BA lead toward the CPT in 3K ohms. (a) 820 DAS Arrangement an installer s option is available to either hold a steady marking condition on BB lead or to allow data to be re-received on BB lead. (b) 86 DAS Arrangement A steady marking condition appears on BB lead. (a) 820 DAS Arrangement CA lead remains connected to CB lead. Holds CC lead OFF towards the CPT. (b) 820 DAS Arrangement Opens CA lead toward the CPT. Holds CB lead and CC lead OFF towards the CPT. Page 4

5 SS, SECTON 32-O-O (5) Lights the TEST lamp. (6) (a) 820 DAS Arrangement Disable local mode if operated. (b) 86 DAS Arrangement No action since no local mode available. (7) Disables HDX local copy option if used. (8) (a) 820 DAS Arrangement f received carrier is present, CF lead is ON towards CPT. Loss of received carrier squelches transmitted carrier and turns CF lead OFF towards CPT. (b) 86 DAS Arrangement CF lead head ON towards CPT. A second operation of the Test key releases the DCE from this mode. A test lamp is provided on the DCE to indicate when the DCE isin the Test Mode as initiated by the above method. An arrangement is provided to allow the use of an external indicator lamp as an installer s option when the DCE is not in view of the attendant. LOCAL MODE 2.05 n order to permit the CPT to be tested through the EA interface interconnection on a local basis, the 820 DAS arrangements provide a Local Mode of operation. This test feature is activated by an ON signal on the CX circuit (Local Mode) except when the DCE is in the Test Mode. When activated, the local mode circuit acts as follows: () (2) (3) (4) Delivers local copy of data placed on the BA circuit to the BB circuit. Clamps the data set transmitter towards the line. marking Opens the received data path of the data set to the BB circuit. Holds the CC circuit OFF toward the CPT. The Local Mode is released an open on the CX circuit. RECEVED CARRER DETECTOR by an OFF signal or OPTON 2.06 An installer s option is provided in the 820 DAS equipped with a Data Set 08arrangement which will allow loss of received carrier to squelch outgoing carrier. This option can be used to automatically notify the telephone company test center that the station has lost its incoming carrier. As discussed in Paragraph 2.05B, in the Test Mode, this action is always provided. 3. TRANSMSSON CHARACTERSTCS OF CHANNEL CHANNEL DSTORTON DEFNTON 3.0 The 50 Baud Channels are normally lined up and maintained by the telephone company using start-stop data characters as a source of test signals. The exception to this is when the CPT always uses synchronous signals and the channel requires regenerative repeaters. The characters generally will be transmitted at the highest rated speed of the channel; namely 50 Bauds. The received signals will be measured in terms of telegraph distortion. Each start-stop data character is composed of several elements; a single unit start element which is always a space, 5, 6 or 7 single unit information elements and sometimes a single unit parity element which may be mark or space, and a stop element which is always a mark and is one unit or longer in length. A typical 8-element character is illustrated in Figure. Telegraph distortion is the measure of the displacement of any mark-to-space or space-to-mark transition from its proper location. The reference point used when measuring telegraph distortion is the initial mark-to-space transition of each character which occurs at the beginning of each start element. The slicing level for all measurements is at about the so~o point on the rising and falling waveforms. Sensing of signal elements is assumed to be timed for the nominal center of each element. The waveforms at the interface meet the rise and decay times specified in RS-232-B. Spurious short duration impulses (on the order of /0 a signal element) are not characteristic of the channel and would be regarded as trouble condition. Page 5

6 SECTON Referring to Figures and 2, transitions measured at the slicing level should occur at integral multiples k from the start transition for no di&xtion. f a transition occurs at a time t earlier or later than this time, the distortion is: Per cent Distortion = At X 00 % For example, refer to Figue 2 and let us examine the distortion of information elment No. 3 which is in the space condition. Assume the nominal element length t. = 0 milliseconds and that & = millisecond and that Ats = 2 milliseconds. Peak Distortion Per Character = At =. x 00 = 2 x 00 = 20fZ0 L 0 Thus, although the element is 30 percent shorter than its nominal length, its telegraph distortion, as defined, is 20 per cent. CHANNEL DSTORTON-FACTORS 3.02 The amount of inherent channel distortion encountered on 50-Baud Channels is a function of the channel length and its complexity (number of transmission links in tandem between any two stations). f the CPT character code format and Baud rate is any one of those listed in Table C, the telephone company may place a regenerative repeater in the channel to insure that it will perform as specified in Paragraph For this reason, the telephone company will generally ask for the speed and code format used by the CPT. However, if the CPT uses the channel for transmitting other codes, variable length bits or characters, or if the CPT uses it alternately at different signaling rates andjor different character code formats, standard regenerative repeaters can not be provided and the inherent distortion of the channel is not specified. Start-Stop TABLE COMMON CHARACTERS Start Element nformation Element-s Stop Element Synchronous Elements COMMON (O-75 Bauds) * Bauds Bauds Bauds 6.2 Bauds Bauds Bauds 75.00,Bauds C DATA DATA FORMATS Unity length Always Space 5, 6, 7, or 8 per character Unity length Mark or Space Unity or greater in length Always Mark Unity length Mark RATES or Space (76-50 Bauds) 0.00 Bauds Bauds Bauds * These data rates may, of course, be used on 50 Baud Channels; however, other channels are available at reduced rates for transmission speeds up to 75 Bauds. These are described in separate Bell System Technical References. PERFORMANCE OBJECTVES 3.o3 The long term objectives of 50-Baud Channels is to have an average performance of error in 0s bits transmitted. The CPT should deliver no more than 5% telegraph distortion at the interface and should be capable of processing received data signals at the interface with up to 40% telegraph distortion. CPT S unable to meet Page 6

7 r SS, SECTON these requirementsmay expect thatspecialengineering and possible associated charges may be incurred. stop pulse of the last received character in a message. [ TURN-AROUND TME HALF-DUPLEX OPERATON 3.04 The nemwmd or local turn-around time of a half-duplex 50-Baud Channel (the required time interval for any telephone company supplied local transmission equipment to condition itself to reverse the direction of transmission) is essentially zero. However, the CPT should not be arranged to reverse its direction of transmission until it has received the entire nominal length The far-end or distant turn-around time of a half-duplex channel (the time interval consisting of the two-way propagation time of the channel, delay through regenerative repeaters and directional controlcircuitoperationin the transmissionequipment) may be as high as 500 milliseconds. However, if far-end turn-around time is critical to the CPT operating procedure, it is recommended that the specific case be discussed with the local telephone company representatives. Page 7

8 SECTON s, o M, * 4 START STOP (Always Space) (Always Mark ) l- + Typical Undistorted Eight Element Start-Stop Figure Signol +s. o M ; t-+ -+ Jt2 At~ Jtl [ - ~ ( A t max ~ loo Peak Dlstortloo =~ te te Per Character 3te 4~ Distorted Eight Element Stcrrt.StOp Signal Figure 2 Page 8

9 EA nterface. ~ AA Protechve Ground ; CPT i. 2 BA Transmitted Data ~ BB Recewed Data A 4 \ CA Request to Send 5, CB Clear to Send 4 6 CC Data Set Readv * 7 AB Signal Ground 8, C F Data Carrier Detector a Data Set Test (For Telco Data Set Test Use only) 2 CX Local Mode (f mplemented) + + Control - 8~0 DAS j i Data Communications Equipment or i DAS ; Mcdem, i s, Data Set i Data and Control Leads nterface or - ~ Test Mode, Local Mode, 7 Local Copy, +8 Functions 49 _l 0 2. Subset } To Line Data Communication Equipment nterface Figure 3 d.

10 SECTON Fig A Data Auxiliary Set (Normally Mounted Vertically) 820D Data Auxiliary Set 08 or 09 Set Equipped with Doto Fig. S--8 6B Data Auxiliary Set Paae 0

11 SS, SECTON 32-O-O Fig. 6-30c Subset (Cover Above) Page

12 SECTON Fig E Data Auxiliary Set Front View 08 Data Data Set Displayed in Front Set and nterface Card nstalled in Set 09 Page 2

13 SS, SECTON 32-O-O Fig. 8A Multiple Data Auxiliary Set Cabinet KS-2008 Page 3

14 SECTON Page 4 4 Pages